The invention relates to high pressure hoses made of elastomers and reinforcements with an inside diameter greater than 50 mm, a continuous longitudinal construction, and any desired length. The invention furthermore concerns methods of manufacturing such high pressure hoses.
It is known to manufacture high pressure hose lines of great length by coupling together a large number of individual lengths. These lengths, however, are short, and the large number of fittings used to assemble them constitute an unacceptable point of weakness and interfere with the cleaning of the line.
In exploration for natural gas and oil in coastal regions conduits are required for the transport of the oil or gas from points of discovery in the ocean to points of use, such conduits consisting normally of steel pipe. In cases where great depths and greatly fissured ocean bottoms are involved, the use of steel pipe is subject to limitations. The flexibility and resilience of steel pipe are inadequate where differences in level are steep or abrupt. In addition, the assembly of steel pipelines in the case of great ocean depths is made difficult by the finite length of the individual steel pipes of 12 to 18 meters on account of the large numbers of annular welds required. At great ocean depths there is also the danger that the great hydrostatic pressure may permanently deform the steel pipes precisely while they are being laid. The wall thicknesses must therefore be proportioned accordingly. A very great volume of freight space must be available for the transportation of the steel pipes to the places where they are to be laid. It is for these reasons that steel pipelines have hitherto been laid only in relatively shallow waters to depths of about 200 meters.
Large tubes made of elastomers and constructed in a manner similar to high pressure hoses are suitable for spanning great ocean depths. Tubes of this kind are used in the high pressure art for the accommodation of high internal pressures at relatively small diameters and short lengths. The technical requirements which must be met by a submarine pipeline at great depths, however, cannot be fulfilled by the hose designs which have been known hitherto. First, of course, materials must be selected for the "pipe design" which are resistant to sea water. The external surfaces of the tubes must not be attacked by sea water even after years of use. In addition, the surface must be so prepared as to inhibit incrustation by sea animals insofar as possible. To span irregular shoals it is necessary to provide lengths of many kilometers, even when the diameters of the tubes are great, and they may be of the order of 300 to 1000 millimeters. It is very important to use the greatest possible individual lengths of tubing in order to reduce the number of welds between the ends of the tubes, insofar as is technically possible.
This goal can be attained, however, only if the transportation problems which occur where large diameters and long transportation hauls are involved are simultaneously solved. A "tube" in the above-named diameter range cannot be transported in the straight condition, with an individual length of, for example, 100 m, by conventional means. It must therefore be wound like a hose in a known manner. At the large hose diameters desired, the drum diameter required for the hose designs known heretofore would also become too large to be transportable.
The known methods of manufacturing high-pressure hoses of laminated materials with a resilient supporting material can be divided basically into the mandrel processes and the mandrel-less processes.
In mandrel manufacturing processes the individual components of the hose, such as the core, the reinforcement and the covering, for example, are applied individually to a mandrel of finite length serving as a mold core. The mandrel length is limited for reasons of easier "strippability," and amounts as a rule to from 20 to 40 meters. In discontinuous manufacturing, a solid steel mandrel is usually used for small hose diameters, and an aluminum tube is used in the case of larger diameters on account of greater ease in handling (German Pat. No. 521,226).
The mandrel-less processes are the only ones which heretofore have permitted the continuous production of hose in any desired because the limitation of length due to the necessity of stripping the hose from the mandrel is eliminated. The construction of the hose in the assembly phase is performed in this case on a slightly compressed fluid, which is air as a rule. The establishment of the hose dimensions is achieved in these processes through the outside diameter in that, prior to the heating, a lead jacket is applied, for example, and is continuously removed again after the heating. In contradistinction to the mandrel process, the accuracy of the inside diameter in this case depends very greatly on the material and machinery parameters. Furthermore, the mandrel-less processes known today are economically applicable only where large quantities of hose and small hose diameters are involved (periodical "Kautschuk und Gummi", February 1963, DK No. 678.06: 621.643.3).
For the manufacture of high pressure hoses of great and very great dimensions, the mandrel process has been used exclusively hitherto. The reason for this is not so much the required constancy of the inside diameter, but essentially two facts: The metal or textile reinforcement necessary for the construction of the hose must be applied under tension, which in the case of the mandrel-less process would result in an unacceptable constriction of the core. An increase of the supporting air pressure is not possible in such cases, since this would likewise result in a deformation of the core, even though it would be in the opposite direction. On the other hand, jacketing with lead during the heating would result in manufacturing costs which would not be economically acceptable.